A conventional microwave heating apparatus provided with a microwave generation part is configured by using a vacuum tube called as a magnetron for the microwave generation part in general as represented by a microwave oven.
A semiconductor element has lower thermal durability in comparison to the magnetron, and thus there is a fear that the element is destructed when exposed to high heat. In case that the microwave generation part formed with using the semiconductor element is developed to the microwave heating apparatus, a circulator forming a circulation type non-reciprocal circuit is used so that high-frequency power amplified in the microwave generation part is supplied to a heating chamber and the high-frequency power is not returned to the microwave generation part. This circulator is formed so as to consume reflected power returned from the heating chamber at a terminal resistance. For example, refer to Japanese Unexamined Patent Publication No. S59-099693.
Also, for example, Japanese Unexamined Utility Model Publication No. S60-019190 discloses an apparatus in which reflected power returned from a heating chamber is consumed by a dummy resistance plate provided on an outer wall surface in an upper part of the heating chamber, and is utilized for retaining heat in the heating chamber.
Further, in order to achieve improvement in heat receiving efficiency, there is an apparatus in which reflected power returned from a heating chamber accommodating an article to be heated to a microwave generation part is detected, and in accordance with a detection value of the reflected power, an oscillating frequency at which the reflected power is minimum is tracked. For example, refer to Japanese Unexamined Patent Publication No. S56-096486.